The usual methods for processing and applying concrete mixtures are shotcrete methods. In these, concrete mixtures are introduced into a concrete spraying machine with which the concrete mixtures are applied via a delivery line to the particular substrate by means of a spray nozzle. Concrete mixtures contain cement, fillers, such as sand or gravel, and optionally further additives.
Dry shotcrete methods and wet shotcrete methods are known in this context. In dry shotcrete methods, concrete mixtures are employed in the dry form (concrete dry mixtures). The concrete dry mixtures are mixed by addition of water in the spray nozzle. In the dry shotcrete method, the concrete compositions obtained in this way are thus sprayed on to a substrate immediately after mixing with water. Polymers, which can be contained in the concrete dry mixture or can also be added only in the spray nozzle, are examples of an additive for concrete mixtures. JP-A 61097152 and JP-A 60152778 disclose that by the use of vinyl acetate/ethylene/vinyl chloride terpolymers in the various dry shotcrete methods, the rebound on application of concrete mixtures to a substrate is reduced. To reduce the formation of dust when carrying out the dry shotcrete method and the associated health hazard to employees on the construction site, JP-A 09-255387 recommends the use of polymers, such as vinyl acetate/ethylene copolymers, in concrete mixtures. For this purpose, JP-A 63-270334 and JP-A 63-002847 propose vinyl acetate/ethylene copolymers which additionally contain units of ethylenically unsaturated carboxylic acids.
In wet shotcrete methods, concrete mixtures are introduced into the concrete spraying machine in an aqueous form (wet concrete mixtures). In this case, the concrete mixtures are thus first mixed with water and then introduced into the concrete spraying machine, with which the wet concrete mixtures are applied via a delivery line with a spray nozzle to a substrate. When the wet,shotcrete method is employed for construction, polymers have hitherto been added in the spray nozzle.
JP-A 11-107506 describes wet shotcrete methods in which vinyl acetate/ethylene/acrylic acid ester terpolymers are added in the spray nozzle in order to reduce the rebound of the wet shotcrete when it impinges on the substrate. DE-A 102007024965 and. DE-A 102007024964 describe polymer-modified setting accelerators and the use thereof in wet shotcrete methods, the polymer-modified setting accelerators being admixed to the wet concrete mixtures in the spray nozzle. JP-A 2004-051422 discloses the use of repair concrete mixtures which are applied by wet shotcrete methods and, in addition to superfine γ-Ca2SiO4, contain vinyl acetate/ethylene copolymers as an additive. In this context, the repair concrete mixtures were employed for renovating concrete by the wet shotcrete methods with subsequent manual working with application thicknesses of up to 2 cm. Concrete compositions containing polyacrylamides with anionic comonomer units are known from EP-A 1726432 for the production of fireproof coatings. DE-A 19723474 describes dry and wet concrete mixtures with emulsifier-stabilized styrene/acrylic acid ester copolymers containing anionically charged monomer units. Such copolymers, nevertheless, are not stable in wet concrete mixtures, the storage stability and therefore the transportation stability as well as the use properties of the wet concrete mixtures suffering as a result. Furthermore, the anionic copolymers also act as plasticizers in wet concrete mixtures as a result of their negative charge. In practice, however, it is advantageous to be able to dose plasticizers and further additives independently of one another, in order to be able to establish precisely the desired concrete properties at each construction section of the particular construction site. Emulsifiers may also have a plasticizing action. The hardened concrete of DE-A 19723474 has an increased elasticity modulus (E modulus), and associated with this a lower elasticity, which can contribute towards cracking of the hardened concrete.
The concrete mixtures known to date and the application thereof by shotcrete methods lead to hardened concrete which is inadequate with respect to its impermeability to water. Hardened concrete is obtained by setting of wet concrete mixtures. Precisely in construction, such as, for example, in tunnel or mine construction, particularly high requirements are imposed on hardened concrete, since the hardened concrete is constantly in contact with, for example, rock or ground water, which furthermore changes markedly in its composition, such as its salt content, depending on the season and the local circumstances, and penetration of which into the hardened concrete severely damages this.
Against this background there was the object of providing hardened concrete which is distinguished by a relatively high impermeability to water and which also overcomes the further problems mentioned above.